The invention relates to a method for forming a structure on a substrate, the method comprising:    providing a substrate, said substrate showing a surface,    repeatedly performing the steps of:            a) adding a thin layer of a fluid with a predetermined thickness on the surface, the fluid forming a solid or liquid layer on the surface, the fluid being a precursor fluid, the layer defining a new surface,        b) converting part of the precursor material to another material or to another physical state by irradiating part of the layer with particles, while the remaining part of the material stays on the surface,            the repeatedly performed steps of a) and b) followed by            c) the removal of material,            the penetration depth of the particles sufficient to convert the precursor material over the complete thickness of one layer, the penetration depth of the particles insufficient to convert the precursor material that, immediately prior to step c), is closest to the substrate,    as a result of which a structure is build in which, prior to step c), unconverted precursor material may be sandwiched between the substrate and converted precursor material.
U.S. Pat. No. 4,575,330 discloses that a 3D object is formed from a fluid in the form of a liquid capable of solidification when irradiated with, for example, a focused beam of light, UV or electrons. By placing a substrate in a container of said liquid in such a way that the surface of said substrate is just submerged, and irradiating a part of the liquid on top of the substrate, said irradiated part of the liquid forms a solidified part adhered to the substrate. The irradiation may, for example, take the form of a focused beam of light, UV or electrons, the beam being scanned over the surface of the liquid in a predetermined pattern. As a result a first layer of solidified material in the form of the predetermined pattern is formed on the substrate. By now repeatedly submerging said structure so that a new thin layer on top of the already solidified material is formed, and exposing a part of the liquid, subsequent layers of solidified material are built upon each other, finally resulting in a solid 3D object submerged in the liquid. The solid 3D object is then taken out of the container with liquid, whereby the non-solidified material is removed.
It is noted that repeatedly submerging the structure may be done by repeatedly lowering the substrate in the container of liquid, or may be done by repeatedly adding liquid to the container, thereby raising the level of non-solidified material in the container. The submerging should for each layer result in the formation of a thin layer with a predetermined thickness so that the dimensions of the structure are well controlled.
It is worth mentioning that the penetration depth of the particles should be more than one layer, so that the different layers overlap and therefore adhere well to each other, but must not be too large as the penetration depth equals the vertical resolution. Typically the penetration depth should be between one and two layer thicknesses.
The known patent mentions the use of electrons from an electron source for irradiating the liquids. However, the known patent fails to give examples of appropriate liquids. As known to the person skilled in the art, for electrons to travel from an electron source to a liquid, the volume between the electron source and the liquid should be evacuated. That the liquid is exposed to vacuum puts severe demands to the evaporation rate of the liquids, and therefore the liquids that can be used. Another problem is that exposing a liquid to a vacuum may change the composition of the liquid due to said evaporation, resulting in undesired effects.
A disadvantage of the known method is that the dimensions of the structures formed are limited by the minimum thickness of the layer of liquid that can be formed on the substrate and/or solidified material. When the predetermined thickness is too small, unreliable wetting of the substrate and/or non-uniform film thickness may result.
Another disadvantage of the known method is that it is limited in the sort of materials that can be used. The materials must be liquids that solidify when irradiated.